Hm, substitute 'miracle' with 'supernatural phenomenon', then.

("supernatural" still in this sense: A "supernatural" explanation appeals to ontologically basic mental things, mental entities that cannot be reduced to nonmental entities.)

So the question of whether lightning is a supernatural phenomenon or not is now about an empirical fact, not about my own ignorance. If the lightning is due to electrically charged regions in clouds, it's natural. If it's due to Thor's rage and only a god can produce it, it's supernatural.

And of course even if we think that lightning is a supernatural phenomenon it could still be Zeus and not Thor ;)